135 / 1971-01-01 00:00:00

Stratigraphy And Paleontology Of Marine Permian And Triassic Sequences In Nong Prue District, Kancha

Marine Triassic,Permian,Bivalve,Ammonoid,Fusulinid,Stratigraphy,Paleontology

The aims of this study are to define the lithostratigraphy of marine Permian and Triassic sedimentary sequences, to identify the bivalve, ammonoid and fusulinid fauna, and to clarify the geological age and the depositional environment. The area of study is located in the Nong Prue District, Kanchanaburi Province, western Thailand. Marine sedimentary sequences in the study area can be subdivided into four rock units, A, B, C and D, from older to younger respectively. The unit A consists of shale, calcareous shale and limestone and contains an ammonoid assemblage in shales. The unit B overlies unconformably on the unit A. It consists of limestone conglomerate, limestone, shale and siliceous shale. Limestone conglomerate contains fusulinid-bearing clasts. The unit C overlies conformably on the unit B and consists of shale and siliceous shale. The unit D overlies conformably on the unit C. It consists of sandstone and shale. A bivalve assemblage has been discovered in shales of Units C and D.
The collected fossils are systematically identified and described. They consist of two Phyla, the Mollusca and the Protozoa. The Mollusca consists of two Classes, the Bivalvia and the Cephalopoda (Ammonoidea). The Bivalvia comprises three genera: Halobia, Posidonia and Daonella. Halobia consists of three species; Halobia (Halobia) talauana Wanner, Halobia (Halobia) styriaca Mojsisovics, and Halobia (Zittelihalobia) sp. The Cephalopoda (Ammonoidea) comprises seven species, i.e., Agathiceras sp., Adrianites sp., Popanoceras sp., Cyclolobus sp., Metalegoceras sp., Parapronorites sp. and Propinacoceras sp. The Protozoa consists of one Class, the Foraminifera which comprises one species: Verbeekina sp.
The age of the unit A is assigned to the Middle Permian (Roadian-Wordian) age based on the ammonoid fauna. The Unit C and D contain the Halobiid bivalve which indicates a Late Triassic (Carnian-Norian) age. The basal conglomerate of unit B contains fusulinid-bearing clasts suggesting that the unit is younger than a late Middle Permian age and is most likely the Triassic based on the stratigraphic ground. Based on the lithological and paleontological evidences, the depositional environments of the studied rock units can be inferred. The unit A consists predominantly of laminated shales which indicate a low-energy environment. These shales contain ammonoids but without associated marine benthic fauna suggesting that they were accumulated far from shore on a deep marine (abyssal plain) environment in the Middle Permian time. The limestone conglomerate in the unit B indicates the main tectonic event of the basin with considerable uplift and erosion which is represented by a strong unconformity after the late Middle Permian time. Shales of units C and D also represent a low-energy environment. They contain only pelagic bivalves (Halobiids) suggesting that they were accumulated on a deep marine (abyssal plain) environment in the Late Triassic time.